From MeritBadgeDotOrg

Like most things in Scouting, the BSA numbering system came about to fill a need. The need was to be able to chart a Scout's progress without having to write out the full names of merit badges in very small spaces.

The first fourteen merit badges, numerically speaking, were the Eagle required merit badges at the time the numbering system originated. The Safety and Sports merit badges are no longer Eagle required while Family Life, Cycling, and Hiking have been added. The remainder of the badges are basically in alphabetical order with newer badges added at the end.

This list also includes discontinued merit badges which were part of the numbering system. These merit badges are provided for reference purposes only. Current merit badges are linked to their requirements pages, discontinued merit badges are not linked.